The historical approach for electrical distribution systems was to use wiring or enclosed ducts with pre-determined fixed access locations for the purpose of adding sub-circuits. These sub-circuits may utilize wire interfaces or plug-in tap boxes at the pre-determined fixed access locations on a busway for additional power taps to serve sub-circuit loads. High density load applications such as data rooms or in industrial plants has evolved to employ continuous access busway tracks to allow for easy and closely spaced addition and removal of the sub-circuit tap boxes at any location without any pre-determined fixed location limitation along the busway lengths. One example of a continuous access busway 10 is illustrated in FIGS. 1A and 1B. Here, the continuous access busway 10 includes elongated electrical contacts 14 within an elongated body 12. A continuous access busway 10 may be considered a “continuous access” busway if it is configured to selectively engage with tap boxes 20 along any portion of the elongated body 12. Notably, in this example, the elongated electrical contacts 14 extend along sidewalls within the busway to receive outwardly extending contacts from a male component of a sub-circuit tap box positioned within the busway, however, other configurations exist where the elongated electrical contacts 14 may extend along the top walls to receive upwardly extending electrical contacts and various other arrangements exist.
A sub-circuit tap box 20 may be an electrical enclosure that distributes power or communication signals from the busway to specific loads. The tap boxes 20 and continuous access busways 10 may be arranged in a variety of ways but be configured to selectively engage along the continuous access busway 10 with a male component 30 that includes electrical conductor contacts (see prior art FIGS. 2A, 2B, 2C, and 2D). The male component 30 may be electrically connected to elongated contacts 14 within the continuous access busway 10 via manual movement of knobs/handles (located on the tap box) or manual manipulation, such as rotation, of the tap box (FIG. 2D) while the male component is positioned within a cavity 16 of the continuous access busway. Some tap boxes (FIGS. 2A, 2B, and 2C) with handles or knobs do not rotate the male component 30 relative to a body enclosure 50, but the knob/handle movements cause the electrical conductor contacts (located on the male component 30) to be either rotated, translated, or otherwise moved into or out of engagement with the elongated electrical contacts 14 within the continuous access busway 10 to selectively communicate electrically. Generally, the continuous access busways 10 include a frame 18 or some other supporting platform that may be along either side of the continuous access busway 10 to allow for structural attachment to the tap box assemblies 20 that is separate from the selective attachment of the electrical contacts from the male component 30 and the elongated electrical contacts 14.
In one example, as disclosed by U.S. Pat. No. 9,564,726, is a tap box with electrical contacts that are manually selectively translated upwardly from the enclosure body to engage contacts facing downwardly within a continuous access busway. In another example, as disclosed by U.S. Pat. No. 7,819,676, the male component of the tab box extends upwardly from the body enclosure and includes contacts that are manually selectively rotated outwardly from a tower sub-assembly to engage contacts aligned within the continuous access busway. In another example, as disclosed by U.S. Pat. No. 9,379,502, is a tap box with a mast head having electrical contacts extending therefrom where a user inserts the mast head within the busway and manually selectively rotates the enclosure body and mast head to engage contacts within the busway. Each of these patents are incorporated by reference in their entireties.
These types of tap boxes 20 may be used in a data room power distribution system wherein the tap box electrically connects a server rack and its internal components to the busway positioned overhead. (See FIG. 3). The busway may be a continuous rail with integrated power, ground, or communication channel contacts. This application as well as others may utilize busway electrical connections that have loads energized from the busway. These applications may be required to be powered while additional loads are added to the busway. Thus, tap boxes may be inserted and electrically connected into the busways while the busway is energized (live work) so that the existing loads are not de-energized. This enables the addition of tap boxes to serve more loads to existing/active busway systems without disruption to applications that require constant power.
Known or existing tap boxes 20, such as the ones described above, require installation personnel to manipulate the tap box with their hands or use their hands by engaging handles/knobs on the tap box or the tap box itself for coupling and decoupling electrical and mechanical contacts from the elongated electrical contacts 14 within the continuous access busway 10. However, if the busway is energized, the users/installers will be in direct contact near the tap box 20 and energized continuous access busway 10 and therefore in potentially dangerous proximity to arc flash and/or projectiles. This would be especially true, if there is a defect within the tap box 20, or the load has defects to which the tap box is connected. Defects may cause very high energy short circuit currents and arcs to occur creating dangerous arc flash and pressures that can also result in projectiles which may not always be contained within the tap box. A defect caused event can also cause a falling injury or electrical exposure to personnel, since the installations are often conducted while personnel are standing on a ladder or other device.
Common defects may include component failures in the tap box or busway or tap loads, short circuit connections within the tap box, faulty components, mis-wiring, unintended safety grounds installed while energizing, unintentional connections to the tap box, incorrect wiring connections within the tap box, electrical failures connected to the tap box, electrical failures within the tap loads, any unintended connections on the load side of the tap box, disengaging the tap box while the loads are energized, etc. Defects or over rated situations during live tap box engagement or disengagement may potentially result in high energy short circuits, or ground fault currents producing arc flash and high arc plasma pressures.
Considering compliance with NFP 70E and other safety standards such as OSHA while performing live work with today's technology, it is suggested to conduct studies including: calculation of the specific installation's energy potential, arc flash zones evaluations, define the arc flash boundary and requirements for personnel to wear Personal Protective Equipment (PPE) while engaging the tap box to an energized busway. It should be noted the PPE has limitations and may only mitigate injuries since personnel are within arm's length of the tap box.
In view thereof, there exists a need for a tap box assembly and system of such design that affords a solution that overcomes the disadvantages of previously known tap box assemblies.